Robot covered with visco-elastic material

Abstract

It is difficult to use in combination a technique of detecting a collision of an arm due to application thereto of an external force and a technique of alleviating the degree of impact of the arm by covering the arm with a cushioning material. This is so because if it is intended to alleviate the impact degree, the timing of detection of the generation of the collision is delayed. The disclosed technique is to overcome the relation of the opposing factors by using a visco-elastic material. Particularly, by selecting the viscosity coefficient and the elasticity coefficient of the material in predetermined ranges, it is possible to alleviate the impact degree without excessive delay of the impact detection timing and forcibly stop the arm before the force acting between the arm and the object exceeds a permissible level.

What is claimed is: 
     
       1. A robot having an arm and an arm driver to move the arm, a surface of the arm subject to collision with an object, the robot comprising a detector for detecting a magnitude of an external force applied to the arm and forcibly stopping the arm driver when the detected magnitude of the external force exceeds a predetermined level, wherein the surface of the arm is covered with a visco-elastic material, wherein the visco-elastic material has a viscosity coefficient and elasticity coefficient, such that the magnitude of the external force acting on the visco-elastic material is less than a permissible level at an instant after lapse of the sum of times t1and t2, where the permissible level does not cause damage to the arm and the object and time t1is measured from the instant when the visco-elastic material is brought into contact with the object until the instant the magnitude of the detected external force reaches the predetermined level acting on the visco-elastic material and time t2is measured from the instant of starting the stopping operation of the arm driver until the instant when the arm is stopped, and the external force acting on the object is F(t)=(ηV+GR)+GV(t-R/V), where F(t) is the external force, η is the viscosity coefficient and G is the elasticity coefficient of the visco-elastic material, R is a radius of a half spherical end of the object, and V is a speed of the arm; and wherein the predetermined level is at a force F(t) =5.0N and the permissible level is at a force F(t)=30.0N, further wherein at t=R/V, R=0.034 m and V=0.6 m/sec and the viscosity coefficient η and the elasticity coefficient G satisfy the following conditions:   5.0N≦Vη+0.6η+0.034G, and at t=R/V+0.15:       30N≧Vη+GR+GV×0.15.